Manual input devices used for navigation and spatial control of a computing system have a significant impact on capabilities of the computer system and a user's overall experience. There are several kinds of manual input devices. The most common of these for personal computers include single-pointer, indirect interaction devices, such as a mouse or trackpad, and direct interaction devices, such as touchscreens.
A single-pointer, indirect interaction device sensor detects user interaction with the sensor and maps this interaction to a position on a display. One method of mapping points of input to the display involves one-to-one mapping of sensor extents directly to the extents of the display, which is called absolute mapping. Examples of devices that employ absolute mapping are pen and touch digitizers. Another method involves mapping device sensor coordinates to a movable subportion of the display, which is called relative mapping.
Examples of devices that employ relative mapping are the mouse and devices that emulate the mouse, such as a trackpad. A mouse senses movement, which is displaces a presumed starting position by a distanced based on the sensed interaction with the device. A trackpad is commonly used in a manner similar to a mouse. The motion of a contact on the trackpad is sensed, and the sensed motion is treated in a manner similar to a mouse input.
A direct interaction device allows interaction with a device that is visually aligned with a display. A direct interaction device maps between positions on a touch sensitive surface and positions on a display of the same size, using an absolute mapping. For example, when a user touches a point on a touchscreen, an input event may trigger an application response, such as command actuation, in the user interface at a position corresponding to the point on the display touched by the user.
Absolute and relative mapping of spatial input from a multi-pointer input device to the display have selective advantages and disadvantages, depending on physical attributes of the input and display devices, the capabilities of the system, the nature and layout of the application user interface, the kind of task the user is performing, and various ergonomic factors.
For example, in a relative mapping mode, the input device sensor can span only a subset of the target display coordinate space. Therefore, navigation from one display location to another location can involve multiple strokes, unless some form of acceleration of the points is applied as movement of the input points is detected. Conversely, in order to achieve pixel-level, point-to-point targeting precision, a form of deceleration of the points can be applied. Such acceleration and deceleration is sometimes referred to as “pointer ballistics.” As another example, in an absolute mapping mode, the input sensor might have a much smaller resolution or large difference in aspect ratio relative to the display coordinate space. Therefore, achieving precision in pixel-level point-to-point navigation can be difficult without some form of positive and/or negative acceleration.